Photographic List Complete List Annual bastard-cabbage Amur corktree Asiatic colubrina Asiatic sand sedge Australian pine Black locust Black swallow-wort Burma reed Bush honeysuckles (exotic) Canada thistle Carrotwood Chinaberry Chinese lespedeza Chinese wisteria Climbing euonymus Cogon grass Common buckthorn Common mullein Common reed English ivy Eurasian watermilfoil Fig buttercup Fire tree Fiveleaf akebia Fountain grass Garlic mustard Goutweed Giant reed Japanese barberry Japanese hop Japanese honeysuckle Japanese knotweed Japanese spiraea Japanese stiltgrass Japanese wisteria Kudzu Leafy spurge Melaleuca Mile-a-minute Multiflora rose Musk thistle Oriental bittersweet Pale swallow-wort Paper mulberry Perennial pepperweed Porcelainberry Princess tree Purple loosestrife Russian-olive Salt cedar Siberian elm Silk tree Smooth cordgrass Spotted knapweed Strawberry guava Tall fescue Tree-of-heaven Velvet tree West Indian marsh grass White poplar Wineberry Yellow Himalayan raspberry Yellow starthistle Aquatics Eurasian watermilfoil Herbaceous Plants Annual bastard-cabbage Asiatic sand sedge Burma reed Canada thistle Cogon grass Chinese lespedeza Common mullein Common reed Eurasian watermilfoil Fig buttercup Fountain grass Garlic mustard Goutweed Giant reed Japanese knotweed Japanese stiltgrass Leafy spurge Musk thistle Perennial pepperweed Purple loosestrife Smooth cordgrass Spotted knapweed Tall fescue West Indian marsh grass Yellow starthistle Shrubs Asiatic colubrina Bush honeysuckles (exotic) Common buckthorn Fire tree Japanese barberry Japanese spiraea Multiflora rose Russian-olive Silk tree Strawberry guava Wineberry Yellow Himalayan raspberry Trees Amur corktree Australian pine Black locust Carrotwood Chinaberry Common buckthorn Melaleuca Paper mulberry Princess tree Salt cedar Siberian elm Silk tree Strawberry guava Tree-of-heaven Velvet tree White poplar Vines Black swallow-wort Chinese wisteria Climbing euonymus English ivy Fiveleaf akebia Japanese honeysuckle Japanese hop Japanese wisteria Kudzu Mile-a-minute Oriental bittersweet Pale swallow-wort Porcelainberry

Fallopia japonica
Buckwheat family (Polygonaceae)
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NATIVE RANGE
Eastern Asia

DESCRIPTION
Japanese knotweed is an upright, shrublike, herbaceous perennial that can grow to over 10 feet in height. As with all members of this family, the base of the stem above each joint is surrounded by a membranous sheath. Stems of Japanese knotweed are smooth, stout and swollen at joints where the leaf meets the stem. Although leaf size may vary, they are normally about 6 inches long by 3 to 4 inches wide, broadly oval to somewhat triangular and pointed at the tip. The minute greenish-white flowers occur in attractive, branched sprays in summer and are followed soon after by small winged fruits. Seeds are triangular, shiny, and very small, about 1/10 inch long.

Japanese knotweed is designated a noxious weed in the State of Washington.

ECOLOGICAL THREAT
Japanese knotweed spreads quickly to form dense thickets that exclude native vegetation and greatly alter natural ecosystems. It poses a significant threat to riparian areas, where it can survive severe floods and is able to rapidly colonize scoured shores and islands. Once established, populations are extremely persistent.

DISTRIBUTION IN THE UNITED STATES
Current distribution of Japanese knotweed includes 36 states in the lower 48 from Maine to Wisconsin south to Louisiana, and scattered midwest and western states. It is not currently known to occur in Hawaii.

HABITAT IN THE UNITED STATES
Japanese knotweed can tolerate a variety of adverse conditions including full shade, high temperatures, high salinity, and drought. It is found near water sources, such as along streams and rivers, in low-lying areas, waste places, utility rights-of-way, and around old homesites. It can quickly become an invasive pest in natural areas after escaping from cultivated gardens.

BACKGROUND
Japanese knotweed was probably introduced to the U.S. in the late 1800's. Also known as crimson beauty, Mexican bamboo, Japanese fleece flower, or Reynoutria, it was first introduced as an ornamental and has also been used for erosion control and for landscape screening. It is now found throughout the eastern U.S., in several western states, and Alaska, which has few exotic invasive plants to date.

BIOLOGY & SPREAD
Japanese knotweed spreads primarily by vegetative means with the help of its long, stout rhizomes. It is often transported to new sites as a contaminant in filldirt seeds, sometimes distributed by water, and carried to a lesser extent by the wind. Escapees from neglected gardens, and discarded cuttings are common routes of dispersal from urban areas.

MANAGEMENT OPTIONS
Grubbing is effective for small initial populations or environmentally sensitive areas where herbicides cannot be used. Using a pulaski or similar digging tool, remove the entire plant including all roots and runners. Juvenile plants can be hand pulled depending on soil conditions and root development. Any portions of the root system not removed will potentially resprout. All plant parts (including mature fruit) should be bagged and disposed of in a trash dumpster to prevent reestablishment. 

Chemical

Cut stem application
Use this method in areas where plants are established within or around non-target plants or where vines have grown into the canopy. This treatment remains effective at low temperatures as long as the ground is not frozen. Cut the stem about 2 inches above ground level.  Immediately apply a 25% solution of glyphosate (e.g., Roundup®, or use Rodeo® if applying in or near wetland areas) or triclopyr (e.g., Garlon) and water to the cross-section of the stem. A subsequent foliar application of glyphosate may be require to control new seedlings and resprouts. 

Foliar application
Use this method to control large populations. It may be necessary to precede foliar applications with stump treatments to reduce the risk of damaging non-target species. Apply a 2% solution of glyphosate or triclopyr and water to thoroughly wet all foliage. Do not apply so heavily that herbicide will drip off leaves. A 0.5% non-ionic surfactant is recommended in order to penetrate the leaf cuticle, and ambient air temperature should be above 65 ºF.

USE PESTICIDES WISELY: ALWAYS READ THE ENTIRE PESTICIDE LABEL CAREFULLY, FOLLOW ALL MIXING AND APPLICATION INSTRUCTIONS AND WEAR ALL RECOMMENDED PERSONAL PROTECTIVE GEAR AND CLOTHING. CONTACT YOUR STATE DEPARTMENT OF AGRICULTURE FOR ANY ADDITIONAL PESTICIDE USE REQUIREMENTS, RESTRICTIONS OR RECOMMENDATIONS. 

NOTICE: MENTION OF PESTICIDE PRODUCTS ON THIS WEB SITE DOES NOT CONSTITUTE ENDORSEMENT OF ANY MATERIAL.

CONTACTS
For more information on the management of Japanese knotweed, please contact:

• Kris Johnson, Great Smoky Mountains National Park, Gatlinburg, TN
• Japanese Knotweed Alliance, http://www.cabi-bioscience.org/html/japanese_knotweed_alliance.htm
• Robert J. Richardson, Aquatic and Noncropland Weed Management, Crop Science Department, Box 7620, North Carolina State University, Raleigh, NC  27695-7620, (919) 515-5653, Rob_Richardson at ncsu.edu

SUGGESTED ALTERNATIVE PLANTS
Many attractive native herbs and shrubs are available that make excellent alternatives to Japanese knotweed. Contact the native plant society in your state for more information.

OTHER LINKS

• Photos at invasive.org
• Invasive Plant Atlas of New England

AUTHOR
Tom Remaley, Great Smoky Mountains National Park, Gatlinburg, TN

EDITOR|
Jil M. Swearingen, National Park Service, Washington, DC

PHOTOGRAPHS
Tom Remaley, Great Smoky Mountains National Park, Gatlinburg, TN
Jil M. Swearingen, National Park Service, Washington, DC

REFERENCES
Ahrens, J.F. 1975.  Preliminary results with glyphosate for control of Polygonum cuspidatum Proceedings of the Northeast Weed Control Conference 29:326. 

Child, L.E., L.C. De Wall, P.M Wade, J.P. Palmer. 1992.  Control and management of Reynoutria species (knotweed). Aspects of Applied Biology 29:295-307. 

Figueroa, P.F. 1989.  Japanese knotweed herbicide screening trial applied as a roadside spray. Proceedings of the Western Society of Weed Science 42:288-298. 

Hirose, T., K. Kitajima. 1986.  Nitrogen uptake and plant growth. I. Effect of nitrogen removal on growth of Polygonum cuspidatum Ann. Bot. 58(4):479-486. 

Japanese Knotweed Alliance

Jennings, V.M, R.S. Fawcett. 1977.  Weed control: Japanese polygonum (Polygonum cuspidatum Sieb. and Zuce.). PM Iowa State Univ. Science Technol. Ames. Coop. Ext. Serv. 762, 2. 

Pridham, A.M.S., A. Bing. 1975.  Japanese bamboo (Polygonum cuspidatum, Polygonum sachalinens). Plants Garden 31(2):56-57. 

Radford, A. E., H.E. Ahles, C.R. Bell. 1968.  Manual of vascular flora of the Carolinas. Chapel Hill, NC: The University of North Carolina Press, 1183. 

Randall, J.R. and J. Marinelli.  1998.  Invasive Plants: Weeds of the Global Garden.  Brooklyn Botanic Garden, Handbook  No. 149, p. 77. 

Scott, R., R.H. Marrs. 1984.  Impact of Japanese knotweed and methods of control. Aspects of Applied Biology 291-296. 

Smith, R.C. 1990.  Polygonum cuspidatum var. compactum American Nurseryman 172(2):142.

Swearingen, J. 2009. WeedUS Database of Plants Invading Natural Areas in the United States: Japanese Knotweed (Polygonum cuspidatum). http://www.invasive.org/weedus/subject.html?sub=3414.

The Nature Conservancy. Japanese Knotweed: Element Stewardship Abstract. In: Wildland Weeds Management & Research Program, Weeds on the Web.

USDA, NRCS. 2009. The PLANTS Database (http://plants.usda.gov). National Plant Data Center, Baton Rouge, LA 70874-4490 USA.